Polycarbonate finds many uses because, in general, articles molded from polycarbonate demonstrate a high level of heat resistance and dimensional stability with good insulating and non-corrosive properties. However, molded polycarbonate articles exhibit decreasing impact resistance in the areas where the article is thicker. Additionally, polycarbonate can be difficult to mold and suffers from the inability to be molded into thinwall products. This disadvantage is somewhat relieved by decreasing the molecular weight of the polycarbonate to lower its viscosity. However, as a result, ductility is often reduced and there is an undesirable increase in gloss. Furthermore, impact resistance for articles molded from polycarbonate declines rapidly at low temperature. Consequently, it is difficult to obtain molded articles from polycarbonate with a good balance of impact resistance over a broad temperature range, heat resistance, dimensional stability, moldability, and controllable gloss.
Various olefin polymers can be blended with polycarbonate to lower the viscosity of the blend. However, blending a polycarbonate with an olefin polymer tends to cause the molded article to delaminate, which reduces impact resistance, toughness, and weldline strength, as reported, for example, in U.S. Pat. No. 4,496,693. This deficiency has been somewhat relieved by the selection of a substantially linear ethylene polymer or a linear ethylene polymer to blend with polycarbonate as disclosed in U.S. Pat. No. 5,416,148 and PCT Pat. No. WO 94/06859. Another resulting disadvantage of blending polycarbonate with various olefin polymers is the tendency to cause pearlesence, which is aesthetically unacceptable, especially in unpainted molded products.
There have been attempts to provide compatibilization in blends of these types. One such method has been graft modification of polyolefin polymers, such as low density, linear low density, or high density polyethylene and polypropylene, with various olefinically unsaturated monomers is well known in the art. Such a modification renders an essentially nonpolar polyolefin material compatible, at least to some limited extent, with polycarbonate. The practice of blending polycarbonate with polyolefin polymers grafted with one or more unsaturated organic compounds containing both ethylenic unsaturation and a carbonyl group, e.g., maleic anhydride and a polyester, is disclosed in U.S. Pat. Nos. 4,840,995 and 4,889,898. The practice of blending polycarbonate with (1) a polyolefin produced by a conventional coordination catalyst, such as a "Ziegler" type or "Philips" type; (2) an epoxide-containing copolymer; and (3) a polyester is discussed in Japanese Pat. Kokai No. H5-39415.
It would be desirable if modifiers blended with polycarbonate for the purpose of improving impact resistance would result in a good combination of heat resistance, dimensional stability, and weldline strength while not increasing the viscosity of the blend or causing delamination as evidenced by peeling or splintering in a molded article. These properties, coupled with controllable gloss and an acceptable "as molded" appearance, as evidenced by the absence of pearlescence, is desired to reduce the need for painting 30 molded articles. Eliminating the need to paint would eliminate the environmental hazards related to painting. Additionally, eliminating painting will reduce the cost to manufacture high performance, aesthetically acceptable molded articles for automotive interior, durable appliances, and electrical applications.